Plasma display panels (hereinafter referred to as PDPs), which are one type of flat panel display, have been developed for practical use and have spread rapidly because of their advantages such as easy upsizing, high-speed display, and low cost.
A commercially available common PDP has a structure in which two glass substrates facing each other, which serve as a front substrate and a rear substrate, each have regularly arranged electrodes and a dielectric layer made of low-melting glass or the like to cover these electrodes. On the dielectric layer of the rear substrate, phosphor layers are provided. On the dielectric layer of the front substrate, a MgO layer as a protective layer is provided to protect the dielectric layer from ion bombardment and to cause secondary electrons to be emitted. A gas containing an inert gas such as Ne or Xe as a main component is sealed into the space between the two substrates and a voltage is applied between the electrodes to generate a discharge, thus causing the phosphors to emit light so that an image is displayed.
There has been a strong demand for high efficiency PDPs. In order to meet this demand, there have been known a method of reducing the dielectric constant of a dielectric layer and a method of increasing the partial pressure of Xe in a discharge gas. The use of these methods, however, causes a problem that a firing potential and a sustaining voltage increase.
It has been known that if a protective layer is made of a material having a high secondary electron emission coefficient, the firing potential and sustaining voltage can be reduced. In this case, a high efficiency PDP can be obtained at low cost because elements having low withstand voltages can be used. For this purpose, it has been considered to use CaO, SrO or BaO, or a solid solution of these oxides instead of MgO, because each of these oxides has a higher secondary electron emission coefficient than MgO even though it also is an alkaline earth metal oxide (Patent Literatures 1 and 2).